The present invention relates to an air cooled condenser installation comprising a first group of heat exchange elements including a plurality of rows of upright tubes impinged by a stream of cooling air and connected at upper and lower open ends by an upper manifold, respectively a lower collecting chamber to each other and a steam conduit communicating with the upper manifold so that the steam flows in downward direction through the tubes and partly condenses, with the condensate flowing in the same direction as the steam, and a second group of heat exchange elements including a second plurality of upright tubes impinged by a second stream of cooling air and connected at upper and lower open ends respectively by an upper chamber and a lower chamber, and a conduit connecting said lower collecting chamber of the first group of heat exchange elements with the lower chamber of said second group of heat exchange elements so that steam which has not been condensed in the first group of heat exchange elements will flow in upward direction through the second plurality of tubes to thereby condense, while the condensate will flow in downward direction in opposition to the flow of steam.
Air cooled condenser installations of the aforementioned kind may be cooled by the surrounding atmosphere or by forced air streams. The heat exchange elements are usually arranged in form of a gable roof. The steam to be condensed is passed first in downward direction through such a heat exchange element or a plurality of such heat exchange elements so that the condensate forming during condensation of the steam will pass in the same direction as the steam, that is in downward direction through the heat exchange element or elements. In order to prevent freezing during operation in wintertime, surplus steam is passed through the heat exchange elements through which steam and condensate flow in the same downward direction and the steam which does not condensate is subsequently condensed in a heat exchange element or a plurality of heat exchange elements in which this surplus steam flows in upward direction to condensate, with the condensate thus formed flowing in downward direction, that is in opposition to the flow of the steam.
If the plurality of heat exchange elements are connected in form of gable roof to each other, the cooling air is blown from below against these heat exchange elements. On the other hand, the heat exchange elements, formed by tubes provided at the outer surfaces thereof with cooling ribs, may also be arranged substantially vertical, in which case the stream of cooling air is passed in a horizontal direction against the heat exchange elements. The heat exchange elements may be arranged in a plurality of rows spaced from each other in direction of the cooling air stream.
It is known that in heat exchange elements in which the condensate flows in a direction opposite to the steam passing therethrough, it is possible that at temperatures below 0.degree. C. hoar frost may form in the upper portions of these heat exchange elements. This formation of hoar frost is due to the fact that in these upper portions of the heat exchange elements a steam-air mixture is present, with a relatively high percentage of air, so that the condensating process will not take place any more in these upper end portions. The moisture contained in the vapor air mixture precipitates therefore at temperatures below 0.degree. C. in the form of hoar frost on the inner surfaces of the tubes through which steam and condensate passes in opposite directions.
At unfavorable operating conditions, for instance during continuous operation at low temperatures, as well as continuous loading of the installation, the danger exists that the thickness of the layer of hoar frost increases more and more until the open cross-section of the tubes, through which steam and condensate passes in opposite direction, is narrowed in such a manner that the non-condensing gases, which accumulate during the condensation process, cannot be completely evacuated. The primary result is an accumulation of air in the heat exchange elements in which steam and condensate pass in opposite directions. Even though these heat exchange elements will not be destroyed, they will not take part any longer in the condensation process and the output is thereby reduced.
A further result of the accumulation of air in part of the heat exchanger tubes, through which condensate and steam pass in opposite direction, may be that now it is not possible any longer to draw through the still acting tubes the necessary amount of steam through the heat exchange element with tubes through which steam and condensate pass in the same direction in order to prevent formation of feared dead zones in the lower portion of the last-mentioned tubes. Such dead zones in the tubes through which steam and condensate pass in the same direction may cause freezing and formation of ice in these tubes, which could lead to damage of the same.
This disadvantage of air cooled condenser installation provided with a first group of heat exchange elements including a plurality of tubes through which steam and condensate pass in the same direction and a second plurality of tubes through which steam and condensate pass in the opposite direction has up to now been obviated in that the heat exchange elements with the tubes through which steam and condensate pass in opposite direction are only intermittently impinged by cooling air. If forced streams of cooling air are used, the ventilators producing the forced cooling air streams are shut down for short moments in intermittent time intervals so that the tubes through which steam and condensate pass in opposite direction are warmed up so that eventually formed hoar frost may be reduced. In the case of cooling the condenser installation by the surrounding air the same effect may be produced, for instance, by covering some of the heat exchange elements through which steam and condensate pass in opposite direction by louvres.
A disadvantage of such an arrangement is that pressure variations will result in the condenser installation, due to the alternating operation of the air cooling during forced air cooling or natural air cooling. The additional work of the operators may be reduced by automating the switching on and off of the ventilators, respectively the actuation of the louvres. However, evidently such an automation can be obtained only with an increased expenditure for control devices.